1. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 1 SIM3302 Software Design & Testing Software Engineering: A Practitioner’s Approach, 6/e Chapter 9 Design Engineering

2. 2 What is design? It's where you stand with a food in two worlds—the world of technology and the world of people and human purposes—and you try to bring the two together... —Mitch Kapor, Dr. Dobbs Journal The Roman architecture critic Vitruvius advanced the notion that well-designed buildings were those which exhibited firmness, commodity, and delight. The same might be said of good software. Firmness: A program should not have any bugs that inhibit its function. Commodity: A program should be suitable for the purposes for which it was intended. Delight: The experience of using the program should be a pleasurable one. Here we have the beginnings of a theory of design for software.

3. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 3 Objectives At the end of this chapter, students should be able to: Define what is design Define what is design Explain the important of design Explain the important of design Explain the design process & design quality Explain the design process & design quality Explain the design principles Explain the design principles Understand the fundamental software design concepts Understand the fundamental software design concepts Explain and give examples for each of the design concepts Explain and give examples for each of the design concepts

4. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 4 Analysis Model -> Design Model

5. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 5 Design and Quality the design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. the design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. the design should provide a complete picture of the software, addressing the data, functional, and behavioral domains from an implementation perspective. the design should provide a complete picture of the software, addressing the data, functional, and behavioral domains from an implementation perspective.

6. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 6 Quality Guidelines A design should exhibit an architecture that (1) has been created using recognizable architectural styles or patterns, (2) is composed of components that exhibit good design characteristics and (3) can be implemented in an evolutionary fashion A design should exhibit an architecture that (1) has been created using recognizable architectural styles or patterns, (2) is composed of components that exhibit good design characteristics and (3) can be implemented in an evolutionary fashion For smaller systems, design can sometimes be developed linearly. For smaller systems, design can sometimes be developed linearly. A design should be modular; that is, the software should be logically partitioned into elements or subsystems A design should be modular; that is, the software should be logically partitioned into elements or subsystems A design should contain distinct representations of data, architecture, interfaces, and components. A design should contain distinct representations of data, architecture, interfaces, and components. A design should lead to data structures that are appropriate for the classes to be implemented and are drawn from recognizable data patterns. A design should lead to data structures that are appropriate for the classes to be implemented and are drawn from recognizable data patterns. A design should lead to components that exhibit independent functional characteristics. A design should lead to components that exhibit independent functional characteristics. A design should lead to interfaces that reduce the complexity of connections between components and with the external environment. A design should lead to interfaces that reduce the complexity of connections between components and with the external environment. A design should be derived using a repeatable method that is driven by information obtained during software requirements analysis. A design should be derived using a repeatable method that is driven by information obtained during software requirements analysis. A design should be represented using a notation that effectively communicates its meaning. A design should be represented using a notation that effectively communicates its meaning.

7. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 7 Design Principles The design process should not suffer from ‘tunnel vision.’ The design process should not suffer from ‘tunnel vision.’ The design should be traceable to the analysis model. The design should be traceable to the analysis model. The design should not reinvent the wheel. The design should not reinvent the wheel. The design should “minimize the intellectual distance” [DAV95] between the software and the problem as it exists in the real world. The design should “minimize the intellectual distance” [DAV95] between the software and the problem as it exists in the real world. The design should exhibit uniformity and integration. The design should exhibit uniformity and integration. The design should be structured to accommodate change. The design should be structured to accommodate change. The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. Design is not coding, coding is not design. Design is not coding, coding is not design. The design should be assessed for quality as it is being created, not after the fact. The design should be assessed for quality as it is being created, not after the fact. The design should be reviewed to minimize conceptual (semantic) errors. The design should be reviewed to minimize conceptual (semantic) errors. From Davis [DAV95]

8. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 8 Fundamental Concepts abstraction—data, procedure, control abstraction—data, procedure, control architecture—the overall structure of the software architecture—the overall structure of the software patterns—”conveys the essence” of a proven design solution patterns—”conveys the essence” of a proven design solution modularity—compartmentalization of data and function modularity—compartmentalization of data and function hiding—controlled interfaces hiding—controlled interfaces Functional independence—single-minded function and low coupling Functional independence—single-minded function and low coupling refinement—elaboration of detail for all abstractions refinement—elaboration of detail for all abstractions Refactoring—a reorganization technique that simplifies the design Refactoring—a reorganization technique that simplifies the design

9. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 9 Data Abstraction door implemented as a data structure manufacturer model number type swing direction inserts lights type type number number weight opening mechanism

10. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 10 Procedural Abstraction open implemented with a "knowledge" of the object that is associated with enter details of enter algorithm

11. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 11Architecture “The overall structure of the software and the ways in which that structure provides conceptual integrity for a system.” [SHA95a] Structural properties. This aspect of the architectural design representation defines the components of a system (e.g., modules, objects, filters) and the manner in which those components are packaged and interact with one another. For example, objects are packaged to encapsulate both data and the processing that manipulates the data and interact via the invocation of methods Extra-functional properties. The architectural design description should address how the design architecture achieves requirements for performance, capacity, reliability, security, adaptability, and other system characteristics. Families of related systems. The architectural design should draw upon repeatable patterns that are commonly encountered in the design of families of similar systems. In essence, the design should have the ability to reuse architectural building blocks.

12. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 12 Patterns Design Pattern Template Pattern name—describes the essence of the pattern in a short but expressive name Intent—describes the pattern and what it does Also-known-as—lists any synonyms for the pattern Motivation—provides an example of the problem Applicability—notes specific design situations in which the pattern is applicable Structure—describes the classes that are required to implement the pattern Participants—describes the responsibilities of the classes that are required to implement the pattern Collaborations—describes how the participants collaborate to carry out their responsibilities Consequences—describes the “design forces” that affect the pattern and the potential trade-offs that must be considered when the pattern is implemented Related patterns—cross-references related design patterns

13. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 13 Modular Design

14. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 14 Modularity: Trade-offs What is the "right" number of modules for a specific software design? optimal number of modules of modules cost of cost of software software number of modules moduleintegrationcost module development cost

15. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 15 Information Hiding module controlled interface "secret" algorithm algorithm data structure data structure details of external interface details of external interface resource allocation policy resource allocation policy clients a specific design decision

16. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 16 Why Information Hiding? reduces the likelihood of “side effects” reduces the likelihood of “side effects” limits the global impact of local design decisions limits the global impact of local design decisions emphasizes communication through controlled interfaces emphasizes communication through controlled interfaces discourages the use of global data discourages the use of global data leads to encapsulation—an attribute of high quality design leads to encapsulation—an attribute of high quality design results in higher quality software results in higher quality software

17. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 17 Stepwise Refinement open walk to door; reach for knob; open door; walk through; close door. repeat until door opens turn knob clockwise; if knob doesn't turn, then take key out; find correct key; insert in lock; endif pull/push door move out of way; end repeat

18. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 18 Functional Independence

19. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 19 Sizing Modules: Two Views

20. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 20 Refactoring Fowler [FOW99] defines refactoring in the following manner: "Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code [design] yet improves its internal structure.” When software is refactored, the existing design is examined for redundancy unused design elements inefficient or unnecessary algorithms poorly constructed or inappropriate data structures or any other design failure that can be corrected to yield a better design.

21. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 21 OO Design Concepts Design classes Design classes Entity classes Entity classes Boundary classes Boundary classes Controller classes Controller classes Inheritance—all responsibilities of a superclass is immediately inherited by all subclasses Inheritance—all responsibilities of a superclass is immediately inherited by all subclasses Messages—stimulate some behavior to occur in the receiving object Messages—stimulate some behavior to occur in the receiving object Polymorphism—a characteristic that greatly reduces the effort required to extend the design Polymorphism—a characteristic that greatly reduces the effort required to extend the design

22. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 22 Design Classes Analysis classes are refined during design to become entity classes Analysis classes are refined during design to become entity classes Boundary classes are developed during design to create the interface (e.g., interactive screen or printed reports) that the user sees and interacts with as the software is used. Boundary classes are developed during design to create the interface (e.g., interactive screen or printed reports) that the user sees and interacts with as the software is used. Boundary classes are designed with the responsibility of managing the way entity objects are represented to users. Boundary classes are designed with the responsibility of managing the way entity objects are represented to users. Controller classes are designed to manage Controller classes are designed to manage the creation or update of entity objects; the creation or update of entity objects; the instantiation of boundary objects as they obtain information from entity objects; the instantiation of boundary objects as they obtain information from entity objects; complex communication between sets of objects; complex communication between sets of objects; validation of data communicated between objects or between the user and the application. validation of data communicated between objects or between the user and the application.

23. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 23 Inheritance Design options: Design options: The class can be designed and built from scratch. That is, inheritance is not used. The class can be designed and built from scratch. That is, inheritance is not used. The class hierarchy can be searched to determine if a class higher in the hierarchy (a superclass)contains most of the required attributes and operations. The new class inherits from the superclass and additions may then be added, as required. The class hierarchy can be searched to determine if a class higher in the hierarchy (a superclass)contains most of the required attributes and operations. The new class inherits from the superclass and additions may then be added, as required. The class hierarchy can be restructured so that the required attributes and operations can be inherited by the new class. The class hierarchy can be restructured so that the required attributes and operations can be inherited by the new class. Characteristics of an existing class can be overridden and different versions of attributes or operations are implemented for the new class. Characteristics of an existing class can be overridden and different versions of attributes or operations are implemented for the new class.

24. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 24 Messages

25. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 25 Polymorphism case of graphtype: if graphtype = linegraph then DrawLineGraph (data); if graphtype = piechart then DrawPieChart (data); if graphtype = histogram then DrawHisto (data); if graphtype = kiviat then DrawKiviat (data); end case; All of the graphs become subclasses of a general class called graph. Using a concept called overloading [TAY90], each subclass defines an operation called draw. An object can send a draw message to any one of the objects instantiated from any one of the subclasses. The object receiving the message will invoke its own draw operation to create the appropriate graph. graphtype draw Conventional approach …

26. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 26 The Design Model

27. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 27 Design Model Elements Data elements Data elements Data model --> data structures Data model --> data structures Data model --> database architecture Data model --> database architecture Architectural elements Architectural elements Application domain Application domain Analysis classes, their relationships, collaborations and behaviors are transformed into design realizations Analysis classes, their relationships, collaborations and behaviors are transformed into design realizations Patterns and “styles” (Chapter 10) Patterns and “styles” (Chapter 10) Interface elements Interface elements the user interface (UI) the user interface (UI) external interfaces to other systems, devices, networks or other producers or consumers of information external interfaces to other systems, devices, networks or other producers or consumers of information internal interfaces between various design components internal interfaces between various design components. Component elements Component elements Deployment elements Deployment elements

28. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 28 Interface Elements

29. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 29 Component Elements

30. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 30 Deployment Elements

31. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 31 Design Patterns The best designers in any field have an uncanny ability to see patterns that characterize a problem and corresponding patterns that can be combined to create a solution The best designers in any field have an uncanny ability to see patterns that characterize a problem and corresponding patterns that can be combined to create a solution A description of a design pattern may also consider a set of design forces. A description of a design pattern may also consider a set of design forces. Design forces describe non-functional requirements (e.g., ease of maintainability, portability) associated the software for which the pattern is to be applied. Design forces describe non-functional requirements (e.g., ease of maintainability, portability) associated the software for which the pattern is to be applied. The pattern characteristics (classes, responsibilities, and collaborations) indicate the attributes of the design that may be adjusted to enable the pattern to accommodate a variety of problems. The pattern characteristics (classes, responsibilities, and collaborations) indicate the attributes of the design that may be adjusted to enable the pattern to accommodate a variety of problems.

32. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 32 Frameworks A framework is not an architectural pattern, but rather a skeleton with a collection of “plug points” (also called hooks and slots) that enable it to be adapted to a specific problem domain. A framework is not an architectural pattern, but rather a skeleton with a collection of “plug points” (also called hooks and slots) that enable it to be adapted to a specific problem domain. Gamma et al note that: Gamma et al note that: Design patterns are more abstract than frameworks. Design patterns are more abstract than frameworks. Design patterns are smaller architectural elements than frameworks Design patterns are smaller architectural elements than frameworks Design patterns are less specialized than frameworks Design patterns are less specialized than frameworks

33. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 33 References Pressman, R. (2003). Software Engineering: A Practitioner's Approach. 6th & 5th edition. New York: McGraw-Hill. Pressman, R. (2003). Software Engineering: A Practitioner's Approach. 6th & 5th edition. New York: McGraw-Hill. Somerville I. (2001). Software Engineering. 6th edition. Addison Wesley Somerville I. (2001). Software Engineering. 6th edition. Addison Wesley ~The End ~